Multilayer optical films have been demonstrated by coextrusion of alternating polymer layers. For example, U.S. Pat. No. 3,610,724 (Rogers), U.S. Pat. No. 4,446,305 (Rogers et al.), U.S. Pat. No. 4,540,623 (Im et al.), U.S. Pat. No. 5,448,404 (Schrenk et al.), and U.S. Pat. No. 5,882,774 (Jonza et al.) each disclose multilayer optical films. In these polymeric multilayer optical films, polymer materials are used predominantly or exclusively in the makeup of the individual layers. Such films are compatible with high volume manufacturing processes, and can be made in large sheet and roll formats. An illustrative embodiment is shown in FIG. 1.
In typical constructions, the film bodies comprise one or more layers of such multilayer optical films, sometimes referred to as an “optical stack”, and further protective layers on one or both sides thereof. Illustrative protective layers include, e.g., so-called “skin layers” on one or both sides comprising more robust materials, e.g., polycarbonate or polycarbonate blends, which impart desired additional mechanical, optical, or chemical properties to the construction. U.S. Pat. No. 6,368,699 (Gilbert et al.) and U.S. Pat. No. 6,737,154 (Jonza et al.) disclose illustrative examples thereof. It is also common to further include additional outer layers for protection, e.g., removable buffer layers sometimes referred to as “premask layers” which protect the film body during early handling and processing and are then removed during later manufacturing steps. Illustrative examples include polyethylene-based films and polyurethane-based films. An illustrative embodiment is shown in FIG. 2.
Many product applications, however, require relatively small and numerous pieces of film. For these applications, small pieces of multilayer optical film can be obtained from a larger sheet of such film by subdividing the sheet by mechanical means, such as by cutting the sheet with a shearing device (e.g., a scissors), or slitting the sheet with a blade, or cutting with other mechanical apparatus (e.g., die stamps and guillotines). However, the forces exerted on the film by the cutting mechanism can cause layer delamination in a region along the cut line or edge of the film. This is particularly true for many polymeric multilayer optical films. The resultant delamination region is often discernable by a discoloration relative to intact areas of the film. Because the multilayer optical film relies on intimate contact of the individual layers to produce the desired reflection/transmission characteristics, as a result of degradation in the delamination region it fails to provide those desired characteristics. In some product applications, the delamination may not be problematic or even noticeable. In others, particularly where it is important for substantially the entire piece of film from edge-to-edge to exhibit the desired reflection or transmission characteristics, or where the film can be subjected to mechanical stresses and/or wide temperature variations that could cause the delamination to propagate in the film over time, the delamination can be highly detrimental.
U.S. Pat. No. 6,991,695 (Tait et al.) discloses a method for using laser radiation to cut or subdivide optical films using, inter alia, removable liners to support the film and cut pieces. Though laser converting of polymeric materials has been known for some time, see, e.g., U.S. Pat. No. 5,010,231 (Huizinga) and U.S. Pat. No. 6,833,528 (De Steur et al.), improvements in regard to laser conversion of optical film bodies are desired.
A typical apparatus will include a laser radiation source that emits suitable laser radiation for the material being cut and a support member for supporting the material in desired orientation to the laser radiation source, e.g., in flat orientation within the effective focus zone. Because of the relatively thin nature of optical films and the narrow field of focus of laser radiation which is used it is important in many instances that the material be held in flat orientation during laser irradation. Stainless steel support members are well known for such use, in part because of the consistently flat configuration which can be attained. Also, it is well known to use support members in a belt configuration to achieve greater operational efficiency and utility.
However, stainless steel can be difficult to keep clean and due to its absorbance characteristics is subject to formation of hot spots which can result in damage to the stainless steel support member or material being cut.
Accordingly, improved support members are desired for laser converting operations, e.g., for use in laser conversion of optical films.